Premature babies’ brains process speech before they’re fully formed

Study shows distinct activity even as neurons are migrating into place.

The human brain has a remarkable capacity for interpreting speech, with large areas of the brain given over to tracking the sound and interpreting it as language. The neurons that manage this capacity are put in place during our embryonic development, and these are able to respond to sounds shortly after birth. But now, a new study looked at brain activity in premature infants, and it showed the networks that respond to syllables are already active well before most infants are normally born.

What makes this all the more remarkable is the networks are still under construction at that time.

The work relied on infants born at about 30 weeks of gestation (normally, birth comes at about 38 weeks). These babies are typically so young they spend most of their time in an intensive care unit, so it's not possible to take them to an MRI tube to track their brain's function. Instead, the researchers took advantage of the human body's relative transparency to certain infrared wavelengths.

It turns out some of these wavelengths are absorbed by different forms of hemoglobin, the oxygen carrier of red blood cells. Using these wavelengths, the authors could distinguish between oxygenated hemoglobin and molecules that had already delivered oxygen to nerve cells. By fitting a light source and series of sensors to the infants' heads, they were able to roughly track where in the brain more of the oxygen was being used, and thus where the brain was most active. The resolution isn't as good as in MRI, but the speech centers of the brain are pretty well mapped, so this wasn't as much of a drawback as it could have been.

Clearly, even full-term infants don't understand speech. But their brains are sensitive to speech, showing increased activity when the syllables change or a new speaker's voice is heard. So, the authors tested both, playing a repeated set of "ba" sounds, but sometimes changing the speaker, or other times slipping in a "ga" instead. And, just as in infants and adults, the activity appeared in specific areas of the brain and showed distinctive left-right differences.

So, the data clearly suggests the ability to process sound associated with speech is already present at 30 weeks after conception. Again, the striking thing about that is the areas of the brain that do this processing aren't fully formed by this point in time.

The areas studied by the author have a distinctive layered structure, formed by the progressive birth and migration of different populations of neurons—those born first for a layer that ever successive population has to migrate through, with the next population forming a second layer that everything after them also has to migrate through. Once the layers are completed, connections among neurons in different layers are formed. At the stage the authors are looking at, the cells are still migrating. Only some initial connections are in place.

It's often difficult to distinguish between the things our brains are structured specifically to do and things our brains are structured to have the capacity to learn. The fact these areas of the brain can pick out speech differences even before the final structure is in place, however, provides some support to the idea that some capacity to speech is inherent to the brain.

17 Reader Comments

Unborn children can most certainly hear outside stimuli. I wonder if the ability to process and then recognize the mother's voice helps to establish the pair bonding between mother and child. It would take time to build that familiarity especially with the brain not yet developed so starting in the womb sounds like a good idea.

As for fMRI - there's a decent Dehaene-Lambertz article from 2006 having 3-month old infants listen to sentences and showing that infants can discriminate repeated sentences. There are also a decent amount of studies by Molfese using ERPs to study language of newborns and using those measures of brain activity to predict later reading and learning ability. This includes one article published in 1980 on preterm infants showing that they easily discriminate between speech and non-speech sounds.

Totally non-scientific study: I used to talk to my (then) unborn first child in-utero all the time. In fact, we also used to play a game. I would poke mommy's belly and say "Poke!" with my head laying somewhere on there. After which my son would "reply" with a poke of his own. We would amuse ourselves like this easily for 20 minutes at a time.

Totally non-scientific study: I used to talk to my (then) unborn first child in-utero all the time. In fact, we also used to play a game. I would poke mommy's belly and say "Poke!" with my head laying somewhere on there. After which my son would "reply" with a poke of his own. We would amuse ourselves like this easily for 20 minutes at a time.

It's awe-inspiring when you realise that an infant is only at the threshold of human capacity for picking up language. Anyone who's had a toddler can't help but be amazed at what we're capable of in that realm. Between late infant-hood (when they start to comprehend language, but cannot speak it as of yet) and the end of the toddler years, it seems like there is no limit to what a human child can learn in communication.

It comes as no surprise that an ability like that has to start its development very early on in the growth cycle. Language is what defines us. Animals can communicate. The brighter ones demonstrate tool use. No other animal - not even dolphins - come even close to the level of communication that humans have evolved.

the networks that respond to syllables are already active well before most infants are normally born.

Amazing, but easy to believe. Little kids seem to be born with innate grammar; they come up with sentences that will startle you and leave you trying to figure out how the kid learned to talk like that.

See Noam Chomsky 50 some odd years ago. Although he obviously couldn't do these types of studies, he realized there is a language faculty that is essentially pre-programmed to acquire and process language, and that language acquisition wasn't "learned" in the traditional sense of the word.

Totally non-scientific study: I used to talk to my (then) unborn first child in-utero all the time. In fact, we also used to play a game. I would poke mommy's belly and say "Poke!" with my head laying somewhere on there. After which my son would "reply" with a poke of his own. We would amuse ourselves like this easily for 20 minutes at a time.

Can confirm this.

Never considered making it into a game, but in the last month of my wife's pregnancy, whenever they fetus was awake and active, it would immediately kick on hearing the sound of her mother's voice, and upon hearing my voice would begin to rotate her whole head and body around inside the womb, or as my wife put it, "Ugh, she's doing the drill again, stop talking!"

If speech went on for a while, the fetus would normally stop after a short time, but after silence fell for more then a few minutes and either her or I started to talk, there we go all over again.

It’s interesting that something can be operational while still being built. While reading this I mentally pictured a brain accompanied by the sound of the Emperor in Return of the Jedi stating “Now witness the language power of this FULLY OPERATIONAL brain!”

See Noam Chomsky 50 some odd years ago. Although he obviously couldn't do these types of studies, he realized there is a language faculty that is essentially pre-programmed to acquire and process language, and that language acquisition wasn't "learned" in the traditional sense of the word.

Love the research! Very cool, very interesting. Too bad there is no way to consider a supernatural explanation, as in a soul or spirit with language abilities using the rudimentary synapse structures to the utmost. But then, by definition, anything supernatural cannot be measured by science.

I wonder if this has any impact on developing the capability for speech.

I was born 6 weeks premature, and nobody heard me speak until I was about 4 years old. Not that I couldn't speak, I just didn't. Apparently, I'd just point to things I wanted and people would get them. The first time my mother heard me speak, it was a full sentence.

I wonder if this has any impact on developing the capability for speech.

I was born 6 weeks premature, and nobody heard me speak until I was about 4 years old. Not that I couldn't speak, I just didn't. Apparently, I'd just point to things I wanted and people would get them. The first time my mother heard me speak, it was a full sentence.

Totally non-scientific study: I used to talk to my (then) unborn first child in-utero all the time. In fact, we also used to play a game. I would poke mommy's belly and say "Poke!" with my head laying somewhere on there. After which my son would "reply" with a poke of his own. We would amuse ourselves like this easily for 20 minutes at a time.

Like your comment, but I think that the point the author was bringing out was that there was more connections to a premie's brain than previously thought. It also explains the reason why a kid whose development is not on par with other kids can achieve some outstanding skills on their own, for example play note for note very difficult note pieces without ever touching a piano. Some kids are exceptional even born premature. Nature always seems to fascinate me when it comes to kids and the things they can accomplish, and this is a prime example of this..